Andy Newman says a recent high-profile hoax on TripAdvisor just demonstrates how unreliable many of its reviews are.

How do you choose which restaurant to eat at when you go out? If you're sensible, you will read the reviews published here every Wednesday, or perhaps consult a respected guide such as Hardens or the AA Restaurant Guide.

Of course, these publications are only giving their own opinions, and you might disagree with them. But at least you can be reassured that they are expressed by people who know about food, and who have actually experienced the establishment in question.

I am constantly mystified as to why so many people instead turn to perhaps the most pernicious and unreliable collection of rubbish available online: TripAdvisor.

Pretty much every chef I have ever met has a tale to tell about diners who munch their way through a whole meal without a murmur, and then threaten to post a negative review on this nasty website unless they receive a discount. This is not restaurant reviewing – it is blackmail.

Three cheers then for Londoner Oobah Butler, who has caused many red faces at TripAdvisor by creating a fictitious restaurant and then successfully conning the website into declaring it the best restaurant in London.

Mr Butler, who tellingly claims to make his living from posting fake positive reviews for £10 a pop, decided to see just how far he could trick TripAdvisor by creating a fake restaurant, complete with slick website and exotic menu.

He called his make-believe restaurant 'The Shed', because it was in fact just that – the shed at the bottom of his garden. He went as far as creating pictures of meals containing such appetising ingredients as bleach, shaving foam and paint – and even his own foot.

By getting all his friends to write fake reviews, the 'restaurant' was soon climbing the rankings. He then noticed an odd phenomenon: reviews started appearing from complete strangers, claiming to have eaten at the newest hot ticket in town (which of course they could not have done, given that it didn't actually exist).

With the endorsement of TripAdvisor, Mr Butler started to get inundated with people trying to book a table, and before long, his 'restaurant' was ranked number on in London on the site.

It's a fun story, and was no doubt the source of much laughter for Mr Butler and his friends, but it raises a serious point: the influence of TripAdvisor is now so great that it can make or break a restaurant, and the living of everybody who works there – often on the basis of reviews written by people who have never been near the place.

Some time ago critic Jay Rayner suggested that people should have to post a scan of their bill before being allowed to put a review on the site, to prove they had at least eaten there. Unsurprisingly, TripAdvisor rejected that sensible proposal, presumably because they knew just what a drop in the number of posts such a measure would cause.

Who knows what percentage of reviews on TripAdvisor are false: posted by restaurants themselves to boost their ratings; negative reviews posted by competitors; malicious reviews by people who failed to secure a discount on their bill; or simply posts written by fantasists and attention-seekers.

A third, a half, three-quarters? We just don't know. All we do know is that someone who makes his living by writing fake reviews for money managed to take a garden shed to the number one spot in the capital, outranking such gastronomic gods as Gordon Ramsay, Heston Blumenthal and Marcus Wareing.

And yet TripAdvisor continues to have a huge influence on where we choose to spend our money. Many people seem to think that the site is some kind of altruistic community, instead of the hard-nosed business it really is.

There is nothing fundamentally wrong with giving a voice to ordinary punters, and some review sites – mainly those which only allow you to post a comment when you have actually booked through them – are very useful sources of opinion.

But as 'The Shed' owner Oobah Butler says, TripAdvisor is 'a weird part of the internet. I'm fascinated with the whole thing. Just how you can manipulate it, but everyone trusts it.'

So next time you think about consulting TripAdvisor about where to eat out, my advice would be to take what it says with a massive pinch of salt.